The present invention relates to a method of waste heat recovery with absorption process, particularly to a method of waste heat recovery with absorption process from a low temperature heat source for power generation or heat collection and use as driving force. The present invention further relates to an apparatus of waste heat recovery in absorption manner and to a gas-salt working fluid such as ammonia-salt working fluid used therein.
In the industrial fields, there is a great amount of waste heat generated, such as flue gas, exhaust gas and process waste heat. Such heat is generally deemed as low grade because its recovery is technically difficult and hard to be implemented. Thus, a lot of low-grade heat sources are wasted. In many petrochemical plants, a great amount of low temperature low-grade heat is discharged, for example, a relatively large flow of hot water usually having a temperature of about 120° C. is discharged from heavy oil catalytic apparatus. As for the heat recovery from such low temperature heat sources, problems related to larger apparatus size, more complicated system and operational and maintenance problems usually exist in conventional steam system due to lower steam pressure and lower energy density. Other low boiling point working media such as hydrocarbons e.g., butane, pentane, have problems such as difficult to condense, poor thermal properties, flammable and environment pollution issues, and usually need multistage large apparatus and high investment and high operating cost due to their low enthalpy value and requirement of greater pressure ratio, so that process efficiency is usually low.
In the prior art, ammonia-water absorption pair as a working medium is proposed for energy recovery and use of low temperature heat sources such as Kalina cyclic power generation. For example, U.S. Pat. No. 4,346,561 discloses a method and apparatus for cyclic energy generation from low-grade heat sources by using ammonia and water as working fluid, and this method is particularly suitable for heat energy conversion of sea water. U.S. Pat. No. 5,029,444 also discloses a method and relevant apparatus for low temperature source cyclic power generation by using a mixed working medium of water and ammonia, wherein the temperature of heat sources usually is 230-400° F. These inventions also have the aforementioned problems caused by the presence of water, and separation unit have to be used for the separation of ammonia and water, so that equipment cost and energy consumption are relatively high.
The object of the present invention is to overcome or reduce at least part of the aforementioned drawbacks or to provide a useful alternative solution.